A known variable valve timing control device is disclosed in JP2016-89664A (hereinafter referred to as Patent reference 1). Patent reference 1 discloses a technology as the variable valve timing control device in which a spool is coaxially disposed with a rotary axis, the variable valve timing control device controlling a relative rotational phase of an advanced-angle chamber and a retarded-angle chamber by controlling a supply and discharge of fluid relative to the advanced-angle chamber and the retarded-angle chamber by operating the spool, the variable valve timing control device controlling an intermediate lock mechanism.
In Patent reference 1, a lock flow path and a lock discharge flow path for controlling the intermediate lock mechanism are provided. The intermediate lock mechanism is unlocked by the supply of the fluid to the lock flow path, and is shifted in a lock state by the discharge of the fluid from the lock discharge flow path.
As disclosed in Patent reference 1, the variable valve timing control device includes the single spool that is coaxially provided with the rotary axis of the variable valve timing control device, and controls the relative rotational phase and the lock mechanism by the operation of the spool. Such a variable valve timing control device can perform an operation having great responsiveness comparing to a variable valve timing control device controlling a relative rotational phase and a lock mechanism by a control valve disposed outside a variable valve timing control device.
Here, assuming the shift of the lock mechanism to the lock state, because Patent reference 1 includes a configuration in which a lock member of the lock mechanism engages with a recessed portion by biasing force of, for example, a spring to reach the lock state, the fluid is required to be discharged from the recessed portion quickly in order to shift the lock mechanism into the lock state with great responsiveness.
However, for example, in Patent reference 1, in a case where the flow path resistance of the lock discharge flow path is high, or in a case where the fluid is inhibited from flowing from the lock discharge path through the discharge flow path inside the spool, the lock mechanism may not quickly shift to the lock state. Specifically, this phenomenon is prominent when the viscosity of the fluid is enhanced at a low temperature.
Here, the difficulty of the shift to the lock state particularly found in the intermediate lock will hereunder be explained. When the relative rotational phase is shifted to the intermediate lock state, the lock shift may be performed in a state where the relative rotational phase is stopped by a vane that comes in contact with a wall portion, such as, for example, in a state of a most retarded-angle lock or a most-advanced angle lock. Comparing to this configuration, when being shifted to the intermediate lock state, the relative rotational phase needs to be shifted quickly to the lock state when a lock member and a lock recessed portion reach an engageable position in a state where the lock member and the lock recessed portion are always relatively displaced from each other. From this reason, shifting to the lock state is difficult.
Further, it is favorable that the variable valve timing control device is downsized in a direction along the rotary axis. However, because the size of the spool is defined by the number of ports supplying and discharging the fluid, and by the control amount of the fluid, the downsizing of the spool has a limit and the further downsizing of the device is difficult.
A need thus exists for a variable valve timing control device which is not susceptible to the drawback mentioned above.